降低转炉总包耐火材料消耗实践|技术前沿
一 转炉优化的具体措施
1、转炉炉型优化
某钢厂210t转炉炉底永久层设计为195mm,炉底工作层镁碳砖厚度为800mm,炉容比0.86m³/t,工作层自中心砖至熔池部位为圆弧平缓过渡，炉底中心砖处于最低位，具体如图1所示。
随着钢铁企业对钢水纯净度的需求提升，近几年来，转炉底吹流量逐渐加大，转炉炉底运行压力大，且从炉底中心开始即起弧砌筑，周边坡度较大，导致转炉在运行过程中炉底从中心砖开始侵蚀，并逐渐扩散至炉底10环。转炉3500炉时残厚为600~700mm(含永久层),侵蚀速率约0.11mm/炉，导致转炉运行过程中维护消耗大，同时影响了转炉运行效率。炉底工作层设计已无法满足钢厂冶炼需求，为此对其炉型进行优化改型，炉底设计见图2。
炉型进行优化调整，炉底1~13环工作层加厚至1000mm。且炉底1~6环形状设计为“平底锅”型，工作层砖紧贴永久层环形砌筑至炉底第6环，自第7环开始缓慢起弧过渡。优化后的设计方案，中心砖不再是最低点，自炉底中心砖至第六环整体为平底，共同承担了钢水的搅拌和静压力。
2、转炉耐材匹配优化
不同的转炉在使用过程中，由于受到不同的铁水成分、冶炼工艺、不同的钢种及辅助设备等诸多因素影响，导致转炉某些局部区域侵蚀下降过快。为降低转炉运行时的侵蚀速率并尽可能使转炉下线时避免出现残厚严重不足的情况，在转炉材质设计过程中对整体或局部进行牌号和材质优化。
国内有研究表明，普通镁碳砖脱碳层厚度是低碳镁碳砖脱碳层厚度的2.4倍。同时，与高碳材料相比，碳含量低的镁碳砖MgO之间颗粒间距小，在材料工作表面容易形成富MgO的反应层4,氧化后镁碳砖更加致密，具有更好的抗氧化性。
3、 转炉终渣控制
采用优质的转炉耐火材料是转炉安全顺行的基础，还与适宜的转炉操作和现场维护密切相关。不同成分铁水Si、Mn、P含量，转炉冶炼枪位等，尤其是溅渣操作及比例、终点成分及终渣控制等，均会对转炉炉衬侵蚀产生一定的影响。
影响转炉炉渣熔点的主要物质有FeO、MgO和碱度。目前某钢厂TFe一般在15%～20%。转炉终渣在一定的TFe比例下，碱度及Mg0%含量越高，渣的熔点就越高，渣越黏稠。从护炉角度来看，对炉衬就越有利，钢厂出于成本角度考虑，转炉碱度一般控制在2.8~3.2。图3和图4分别展示了某钢厂优化前后210t转炉终渣的碱度及MgO含量，优化前及优化后终渣碱度由2.9提升至3.3,终渣MgO含量由5.8%提升至6.5%。
二 应用效果应用效果
1、侵蚀速率下降
某钢厂210t转炉优化前全炉役炉底测厚数据如图3所示。炉底侵蚀速率为0.046mm/炉，下线时炉底工作层厚度约400mm。转炉在运行前期中心砖周边1.5m范围内侵蚀明显较快。
采取炉底炉型优化、合理的耐材匹配及转炉终渣控制等一系列措施后，7525炉下线。全炉役测厚数据如图4所示，侵蚀速率为0.037mm/炉，侵蚀较优化前明显减慢，且转炉运行前期未出现中心砖明显下降的状况，底吹元件与转炉同步下线。
2、维护消耗下降
采取炉底炉型优化、合理的耐材匹配及转炉终渣控制等一系列措施后，转炉维护材料消耗。后大面维护材料自0.4kg/t钢降至0.35kg/t钢，下降0.05kg/t钢;炉底维护吨钢消耗自0.25kg/t钢降至0.17kg/t钢，下降0.08kg/t钢。转炉维护总消耗合计下降0.13kg/t钢。炉役合计减少维护消耗210t。
3、 转炉利用效率提升
随着转炉维护材料消耗下降，转炉维护时间随之下降，转炉用于维护的时间占比如图5所示。后大面维护时间减少41h,炉底减少66h,共计节省维护时间107h。由于提升转炉溅渣比例，导致增加38h,转炉维护占总运行时间的比值自13.8%下降至13.2%，转炉利用效率提升0.6%。
三 结论
1、对于某钢厂平底型转炉炉壳，炉底设计为平底型炉型能减缓炉底中心的侵蚀速率，通过对炉底工作层自800mm加厚至1000mm,并改变炉型，全炉役炉底平均侵蚀速率由0.11mm/炉降至0.085mm/炉，降低比例为22.7%。
2、对于低碳钢冶炼的转炉，适当减少炉底及后大面镁碳砖碳含量，可减缓炉底及后大面侵蚀。
3、适当调整转炉终渣碱度及MgO含量，提高全炉役溅渣比例可有效减少转炉维护。
4、采取炉底炉型优化、合理的耐材匹配及转炉终渣控制等一系列措施后，某钢厂210t转炉维护总消耗合计下降0.13kg/t钢。
Practice of reducing the consumption of refractory materials in Bessemer main package | technology frontier
Specific measures for the optimization of a converter
1.Optimization of converter type
The permanent layer at the bottom of 210t converter in a steel plant is designed to be 195mm, the thickness of magnesia carbon brick at the bottom of the working layer is 800mm, and the furnace volume ratio is 0.86m³/t. The working layer has a gentle arc transition from the central brick to the melting pool, and the central brick at the bottom of the furnace is at the lowest position, as shown in Figure1.
With the increasing demand of steel enterprises for the purity of molten steel, in recent years, the blowing flow rate of the converter bottom has gradually increased, the operating pressure of the converter bottom is large, and the arc masonry starts from the center of the converter bottom, and the surrounding slope is large, resulting in the erosion of the converter bottom from the center brick during operation and gradually spread to the 10th ring of the converter bottom. When the converter is 3500, the residual thickness is 600~700mm(including permanent layer), and the erosion rate is about 0.11mm/ furnace, which leads to large maintenance consumption during the operation of the converter and affects the operation efficiency of the converter. The design of the working layer of the furnace bottom can no longer meet the smelting needs of steel mills, so the furnace shape is optimized and modified, and the design of the furnace bottom is shown in Figure 2.
The furnace type was optimized and adjusted, and the working layer of 1-13 rings at the bottom of the furnace was thickened to 1000mm. In addition, the shape of 1-6 rings at the bottom of the furnace is designed as “pan” type, and the working layer bricks are laid in a ring close to the permanent layer to the sixth ring at the bottom of the furnace, and the arc transition starts slowly from the seventh ring. In the optimized design scheme, the central brick is no longer the lowest point, and the whole bottom is flat from the central brick to the sixth ring, which jointly bears the stirring and static pressure of the molten steel.
2、Matching and optimization of resistant materials of converter
Due to the influence of different molten iron composition, smelting process, different steel grades and auxiliary equipment, the erosion in some local areas of the converter decreases too fast. In order to reduce the erosion rate of the converter during operation and avoid the serious lack of residual thickness when the converter is offline as much as possible, the overall or partial grade and material optimization are carried out in the material design process of the converter.
Domestic research shows that the decarburization layer thickness of ordinary magnesia carbon brick is 2.4 times that of low carbon magnesia carbon brick. At the same time, compared with high-carbon materials, the particle spacing between MgO bricks with low carbon content is small, and MGO-rich reaction layer 4 is easily formed on the working surface of the material. After oxidation, MGO-carbon bricks are denser and have better oxidation resistance.
3、 Converter final slag control
The use of high quality refractories is the basis for the safe running of the converter, and is closely related to the proper operation and on-site maintenance of the converter. The content of Si, Mn and P in hot metal with different components, the position of the gun in the converter, especially the operation and proportion of slag splashing, the composition of the end point and the control of the final slag, all have a certain influence on the erosion of the converter lining.
The main substances that affect the melting point of the slag of converter are FeO, MgO and alkalinity. At present, the TFe of a steel mill is generally 15% ~ 20%. Under a certain proportion of TFe, the higher the alkalinity and Mg0% content of the final slag, the higher the melting point of the slag and the thicker the slag. From the perspective of furnace protection, the more favorable it is to the lining, and the basicity of the converter is generally controlled at 2.8~3.2 for the sake of cost. Figure 3 and Figure 4 respectively show the basicity and MgO content of 210t converter final slag before and after optimization of a steel plant. The basicity of final slag before and after optimization is increased from 2.9 to 3.3, and the MgO content of final slag is increased from 5.8% to 6.5%.
Application Effect Application effect
Erosion rate decreases
The thickness measurement data of the bottom of the full-service 210t converter before optimization of a steel mill is shown in Figure 3. The erosion rate of the bottom of the furnace is 0.046mm/ furnace, and the thickness of the working layer of the bottom of the furnace is about 400mm. In the early stage of operation, the erosion around the center brick is obviously faster within 1.5m.
After adopting a series of measures, such as optimization of furnace bottom shape, reasonable matching of resistant materials and control of final slag of converter, 7525 furnace goes offline. The thickness measurement data of the whole furnace in service is shown in Figure 4. The erosion rate is 0.037mm/ furnace, which slows down significantly compared with that before optimization. In addition, the center brick does not decline significantly in the early stage of operation of the converter, and the bottom blowing element and the converter go down simultaneously.
2、Decrease in maintenance consumption
After adopting a series of measures, such as optimization of furnace bottom shape, reasonable matching of resistant materials and control of final slag of converter, the material consumption of converter maintenance is improved. After the large surface maintenance material from 0.4kg/t steel to 0.35kg/t steel, decreased by 0.05kg/t steel; The consumption of tonnage steel for furnace bottom maintenance decreased from 0.25kg/t steel to 0.17kg/t steel, a decrease of 0.08kg/t steel. The total consumption of converter maintenance decreased by 0.13kg/t steel. Total maintenance consumption of furnace service is reduced by 210t.
3、The utilization efficiency of converter is improved
As the consumption of maintenance materials of the converter decreases, the maintenance time of the converter decreases accordingly, as shown in Figure 5. The maintenance time of the rear surface is reduced by 41h, the bottom of the furnace is reduced by 66h, and the total maintenance time is saved by 107h. Due to the increase of slag splashing ratio of converter, resulting in an increase of 38h, the ratio of converter maintenance to the total operating time decreased from 13.8% to 13.2%, and the utilization efficiency of converter increased by 0.6%.
Conclusion
1.For the flat-bottom converter shell of a steel mill, the flat-bottom furnace bottom design can slow down the erosion rate of the center of the furnace bottom. By thickening the working layer of the furnace bottom from 800mm to 1000mm and changing the furnace type, the average erosion rate of the whole furnace bottom in service can be reduced from 0.11mm/ furnace to 0.085mm/ furnace, with a reduction ratio of 22.7%.
2. for the converter of low carbon steel smelting, the carbon content of the bottom and the large surface magnesia carbon brick is properly reduced, which can slow down the erosion of the bottom and the large surface.
3.Properly adjusting the basicity and MgO content of the final slag of the converter and increasing the proportion of splashing slag in the whole furnace can effectively reduce the maintenance of the converter.
4.After taking a series of measures such as optimization of furnace bottom furnace shape, reasonable matching of resistant materials and control of final slag of converter, the total maintenance consumption of 210t converter in a steel mill decreased by 0.13kg/t steel.
